Facilitating seamless transitions in flexible microgrids: A unified control systems framework for enabling multi-mode inverters

The increasing integration of renewable energy sources into the power grid offers both opportunities and challenges for grid performance, stability, and reliability. Inverter-based microgrids offer a promising solution for the large-scale integration of renewable resources, which often come with a high degree of uncertainty. However, the current state-of-the-art typically employs highly specialized control algorithms and operation modes for the comprising DC/AC inverters, particularly in the primary control layer. This approach hinders the true potential of flexible microgrids to dynamically respond to changing generation and consumption profiles, grid faults, and contingency events. This dissertation investigates a novel integrated control framework for DC/AC inverter that is capable of achieving seamless transitions among a spectrum of operational modes, including grid-forming (GFM), grid-following (GFL), static synchronous compensator (STATCOM), energy storage system (ESS), and voltage source inverter (VSI). This is achieved by proposing a control architecture that is common to all operating modes. The proposed architecture is then equipped with a rigorous framework for stability and performance analysis that accurately captures the effects of MIMO coupled dynamics on stability and performance. Consequently, it provides simpler yet robust guidelines for stability, robustness, and performance analysis and design, in terms of equivalent SISO system and irrespective of the specific operating mode. Within the proposed control architecture, distinct modes are defined by two control variables leading to a two-dimensional continuum of operating modes. This operating space facilitating seamless transitions trajectories between modes by dynamically altering these variables towards corresponding operation setpoints. Stability, robustness, and fundamental limitation analyses are provided for the closed-loop system across any mode, as well as during transitions between modes. This design facilitates stable and enhanced on-grid integration, even during GFM mode operation. Ultimately, we demonstrate the key attributes of the proposed framework through extensive simulations and experiments, designed to highlight its efficacy in managing on-grid operation and islanding scenarios, particularly in situations of weak grid operation.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Askarian, Alireza

Contributors dc:contributor

• Salapaka, Srinivasa M
• Stillwell, Andrew R
• Banerjee, Arijit
• Bose, Subhonmesh

• Active damping, asymmetrical fault, Bode sensitivity, control systems, grid-following (GFL) inverter, grid-forming (GFM) inverter, harmonic, microgrids, multi-input multi-output (MIMO) systems, phase-locked loop (PLL), robust stability, seamless transition, virtual impedance, virtual inertia, weak grid.

Statement dc:rights

• Copyright 2024 Alireza Askarian

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/129650

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/129650